With the development of communications technologies, a modem, which is a core chip in a communication device, is also being upgraded. Therefore, modems from several generations coexist in a communication network. A modem from a new generation needs to ensure effective compatibility with a modem from a previous generation; furthermore, an operator needs to configure a modulation mode of the modem from a new generation as a current working modulation mode of a peer modem, which means complex operations, and as a result, efficiency of network deployment is reduced.